This invention relates to improvements in a photosensitive material processing apparatus.
A photosensitive material processing apparatus in which the photosensitive material is developed, fixed, washed, and dried in a drying unit as it is being conveyed, is used to process the exposed photosensitive material.
There are two conventional systems to dry photosensitive materials. One is the hot air current type drying system in which a hot air current is blown against the photosensitive materials and the other is the infrared type drying system in which the photosensitive materials are irradiated with infrared rays. The drying system is an important factor for a photosensitive material processing apparatus to improve image quality, to increase its processing capacity, to cut down on its energy consumption, and to simplify its structure so as to be made compact. In the hot air current type drying system, it takes a long time to dry the photosensitive materials, although the system has the advantage of being able to dry the photosensitive materials gently and uniformly, and to obtain a high quality image. In order to reduce the drying time, some measures can be considered such as extending the photosensitive material conveying passage in the apparatus or providing a heater with greater heating capacity to the apparatus. However, these measures inevitably lead to a large size apparatus and an increase in energy costs.
In the case of the infrared type drying system, the drying temperature can be kept high to increase the drying capacity. On the other hand, there are disadvantages in this system; there is a difference in the residual water between the black portions of the photosensitive material and the white portions; and when the photosensitive material is dried completely in this system, the gelatin layer either of the black portion or of the white portion is hardened earlier than a mediumly exposed portion of the photosensitive material, and glitters to deteriorate image quality.
In order to solve this problem, the inventors made a study of film drying and found that the residual water ratio of the photosensitive materials and the surface temperature vary as the drying time goes by. As a result, the inventors could draw graphs which show the relation between the residual water ratio and the drying time and the relation between the surface temperature of the photosensitive material and the drying time. They are shown in FIG. 1.
The graph shown in FIG. 1 can be explained as follows.
The solid line in FIG. 1 shows the variation of the residual water ratio with the lapse of time. Since the drying time is equal to 0 at the point of intersection of the left longitudinal axis and the solid line, the residual water ratio of the photosensitive material is equal to 100%.
The broken line in FIG. 1 shows the variation of the photosensitive material surface temperature, which varies with the lapse of time. The point of intersection at which the right longitudinal axis and the broken line intersect, shows the temperature of the drying unit.
The following can be known from FIG. 1.
(1) Although the residual water ratio of the photosensitive material decreases with the lapse of time, the surface temperature of the photosensitive material is constant until the residual water ratio of the photosensitive material reaches a predetermined value.
(2) When the drying time exceeds a predetermined value, the residual water ratio of the photosensitive material gently decreases. However, the photosensitive material surface temperature increases to the temperature of the drying unit.
Giving consideration to the facts (1) and (2) described above, it can be understood that there are two drying regions in drying of photosensitive materials. These regions are defined as the drying-rate-constant-region and the drying-rate-decreasing-region in this specification.
In the drying-rate-constant-region, the heat quantity necessary to evaporate the water which is attached to both sides of the photosensitive material, which will be called `latent heat for evaporation` of water attached to the surface of the photosensitive material hereafter, is larger than the heat quantity necessary to extract the water contained in the photosensitive emulsion to the surface of the photosensitive material, which will be called `heat for diffusion` of the water contained in the emulsion layer hereafter. Referring to the solid line in FIG. 1, the residual water volume in the photosensitive material decreases with the lapse of time. However, referring to the broken line in FIG. 1, the photosensitive material surface temperature is kept almost at constant temperature tw.degree. C. which is lower than the drying air temperature t.degree. C.
The drying-rate-decreasing-region is defined as the region in which `heat for diffusion` necessary to extract the water contained in the emulsion layer of the photosensitive material to the surface, is larger than the `latent heat for evaporation` necessary to evaporate the water attached to both sides of the photosensitive material. Consequently, `latent heat for evaporation` to evaporate the water removed to the surface of the photosensitive material, becomes smaller and the heat quantity to increase the photosensitive material surface temperature becomes larger. As a result, the photosensitive material surface temperature is increased to the hot air temperature t.degree. C. which is used to dry the photosensitive material. This is shown by a broken line in FIG. 1.
In the drying-rate-decreasing-region, as the water in the emulsion layer is decreased, `heat for diffusion` is also decreased. Finally, the water contained in the emulsion layer becomes almost 0. It is the end of drying of the photosensitive material.
The photosensitive material residual water containing rate at the boundary between the drying-rate-constant-region and the drying-rate-decreasing-region, is defined as the critical water content and the boundary is defined as the critical water content point.
To explain in more detail, the critical water content point is the limited point at which `latent heat for evaporation` is constant. To put it concretely, the critical water content point is the point at which the water attached to the photosensitive material surface becomes almost 0 during the drying process.
FIG. 1 shows an example in which the SR film manufactured by Konica was used as the photosensitive material, wherein the drying unit temperature t was kept at 45.degree. C. and the relative humidity was kept at 40%. In this case, the critical water content was 10 to 25% and the photosensitive material surface temperature tw in the drying-rate-constant-region was 32.degree. C.
The critical water content rate differs with various photosensitive materials according to the thickness of the emulsion layer, the composition, and the structure of the layers. The value of tw also differs with various photosensitive materials and the drying conditions.
Giving consideration to the above, the inventors have found the facts relating to drying of the photosensitive materials as follows: in the hot air current type drying system, it takes a long time to dry the photosensitive materials in the drying-rate-constant-region; in the infrared type drying system, it is possible to reduce the drying time in the drying-rate-constant-region; but the uneven drying is caused by that the photosensitive materials are dried to an extreme extent in the drying-rate-decreasing-region.
The object of the present invention is to solve the problems described above and to provide an improved photosensitive material processing apparatus by making use of the characteristics of both the hot air current type drying system and the infrared type drying system, in order to reduce the drying time of the photosensitive materials so as to improve the processing capacity and to improve image quality by drying the photosensitive materials uniformly.